Method for cooling a plasma electrode system for an etching apparatus

ABSTRACT

An etching method comprises the steps of setting a substrate to be processed above the surface of a first electrode opposed to a second electrode within a vacuum container, with a clearance formed between the surface of the first electrode and the substrate, supplying a cooling gas to the electrodes with a predetermined flow rate and a pressure, supplying a process gas into the vacuum container, changing the process gas to a plasma, by applying a predetermined electric power across the electrodes, and etching the substrate by means of the plasma of the process gas.

CROSS-REFERENCE TO THE RELATED APPLICATION

This application is a continuation-in-part, of application Ser. No.298,892, filed on Jan. 19, 1989, now U.S. Pat. No. 4,963,713.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an etching method.

2. Description of the Related Art

The plasma etching apparatus which uses reaction components in gasplasma has attracted attention these days as a means for etching variouskinds of thin films. This etching apparatus can make the complicatedmanufacturing process of semiconductor elements simple and automatic.Further, it can create semiconductor elements of micropattern which highprecision.

According to this etching apparatus, a block electrode made of aluminiumis located at the lower portion of an air-tight container which iscommunicated with a vacuum means. Another block electrode made ofaluminium and provided with an electrode made of amorphous carbon islocated above the lower block electrode in the air-tight container. RFpower source is connected to the electrode made of amorphous carbon andthe upper block electrode made of aluminium. A substrate to be treated,that is, a semiconductor wafer is mounted on the lower block electrodemade of aluminium. Power is applied to the RF power source and to theelectrodes, while a desired processing gas is supplied between the upperand lower block electrodes at the same time. The processing gas is thuschanged to plasma by the electric power applied. The surface of thesemiconductor wafer is etched by the processing gas which has beenchanged to plasma.

In the case of the above-mentioned plasma etching apparatus, however,electric power is applied to the electrodes to change the processing gasto plasma. The semiconductor wafer is heated by energy created at thetime when the processing gas is changed to plasma. The resist layer onthe semiconductor wafer is damaged by this heat. It is therefore neededthat the semiconductor wafer is cooled while it is being etched.Preliminarily-opened Japanese Patent Application Sho 61-20622, forexample, discloses a technique of cooling the semiconductor wafer andthe like. According to this technique, the semiconductor wafer ismounted on the electrode while it is pressed along its peripheral rim. Acooling gas is supplied between the semiconductor wafer and theelectrode to spread from the center of the wafer to the peripherythereof so as to cool the semiconductor wafer. The cooling gas issupplied, in this case, to the underside of the semiconductor wafer onlyto spread from the center of the wafer to the periphery thereof.Therefore, the pressure and flow rate of the cooling gas differ withdifferent positions on the underside of the semiconductor wafer. Thesemiconductor wafer is thus sometimes lifted from the electrode to makesmaller its area which is contacted with the electrode. This makes itimpossible to apply uniform etching to the whole surface of thesemiconductor wafer.

Electric power is applied to both of the block electrodes in theconventional plasma etching apparatus. The upper block electrode isheated to 150° to 180° C. in this case. The electrode made of amorphouscarbon and the upper block electrode provided with thisamorphous-carbon-made electrode are expanded by heat. Amorphous carbonis different from aluminium in thermal expansion coefficient. Thiscauses the amorphous-carbon-made electrode to be cracked.

Japanese Patent Publication Sho 62-48758 discloses a technique ofcooling the electrodes to eliminate the above-mentioned drawback.According to this technique, electric power is applied to the blockelectrodes while the amorphous-carbon-made electrode is being cooled.This prevents the electrode from being cracked. When electric power isapplied to the block electrodes while the electrode is not being cooled,however, the amorphous-carbon-made electrode is still cracked because ofthermal expansion.

SUMMARY OF THE INVENTION

An object of the present invention is to provide an etching methodcapable of applying uniform etching to a matter to be processed bycontrolling the pressure and flow rate of a cooling gas.

Another object of the present invention is to provide an etching methodcapable of preventing the electrode from being cracked by thermalexpansion to enhance its durability.

The present invention is intended to provide an etching methodcomprising an etching method comprising the steps of setting a substrateto be processed above the surface of a first electrode opposed to asecond electrode within a vacuum container, with a clearance formedbetween the surface of the first electrode and the substrate; supplyinga cooling gas to the electrodes with a predetermined flow rate and apressure; supplying a process gas into the vacuum container; andchanging the process gas to a plasma, by applying a predeterminedelectric power across the electrode and etching the substrate by meansof the plasma of the process gas.

The cooling gas, which is supplied to cool the electrodes, may be usedalso as a supporting gas for supporting the substrate to be processedabove one of the electrode.

A process of controlling the flow rate and pressure of the cooling gasmay be included in the cooling gas supply process.

Further, the process of changing the processing gas to plasma mayinclude a process of causing the electrodes to stop the generation ofplasma when it is detected that the electrodes are not cooled to thedesired extent.

According to the etching method of the present invention, the substrateto be processed is cooled by controlling the flow rate and pressure ofthe cooling gas which is supplied between the substrate and the blockelectrode so as to support the substrate above the block electrode bythe pressure of the cooling gas. The temperature of the substrate ismade equal at every point on the substrate since the cooling gas isfilled between the substrate and the block electrode. Etching is appliedto the substrate while it is kept under this state, thereby enabling theuniformity of etching to be enhanced.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view showing an example of the etching apparatusused in the present invention;

FIGS. 2A, 2B and 2C are graphs showing how the surface temperature ofthe semiconductor wafer changes when the flow rate and pressure of thecooling gas are changed in the etching apparatus shown in FIG. 1;

FIG. 3 shows a system for controlling the flow rate and pressure of thecooling gas in the etching apparatus shown in FIG. 1;

FIGS. 4A and 5A show positions of those holes through which the coolinggas is supplied in the etching apparatus shown in FIG. 1;

FIGS. 4B and 5B are graphs showing the relation between wafertemperature and clamp-driving pressure; and

FIG. 6 shows an arrangement of the means for stopping the generation ofplasma.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

An embodiment of the present invention will be described.

FIG. 1 is a sectional view showing an example of the etching apparatusused in the method of the present invention.

Block electrode 4 which ca be lifted by lift system 2 is located at theupper portion of reaction container 1 made of conductive material suchas aluminium and having a surface processed with anodized aluminum. Liftsystem 2 includes an air cylinder, a ball screw and connecting rod 3,and container 1 is made air-tight. Block electrode 4 is made ofconductive material such as aluminium and its surface is processed withanodized aluminum. Block electrode 4 has a cooling means, which includespassage 5 extending through block electrode 4. Passage 5 is connected toa cooling device (not shown), which is located outside the reactioncontainer 1, through pipes 6 and liquid such as water which has acertain temperature is circulated through pipes 6 and passage 5. Thecooling means uses liquid as its cooling medium, but it may be a forcedair cooling means which circulates cooled air, a natural air coolingmeans which uses radiating fins located adjacent to block electrode 4,or a electric cooling means which uses Peltier effect elements arrangedin block electrode 4.

Upper electrode 7 made of amorphous carbon, for example, is locatedunder block electrode 4 and it is electrically connected to the latter.A little space 8 is formed between upper electrode 7 and block electrode4 and gas supply pipe 9 is communicated with this space 8. Reaction gassuch as argon and freon is supplied from a gas supply source (notshown), which is located outside the reaction container 1, into space 8through gas supply pipe 9 Upper electrode 7 is provided with pluralholes 10 which allow the reaction gas in space 8 to flow into the insideof reaction container 1 through upper electrode 7. Insulating ring 11encloses upper and block electrodes 7 and 4. Sealing ring 12 extendsfrom the underside of insulating ring 11 to the peripheral rim of theunderside of upper electrode 7. Sealing ring 12 is made of insulatingmaterial such as ethylene tetrafluoride resin in such a way that plasmacan be generated to have substantially same radius as that of asubstrate or semiconductor wafer etched.

Semiconductor wafer 13 is mounted above the surface of lower blockelectrode 14 which is opposed to upper electrode 7. Lower blockelectrode 14 is made of aluminium, for example, having its surfaceprocessed with anodized aluminum and it is made flat. The upper surfaceof lower block electrode 14 is curved (R) or convexed, sloping from itstop down to its peripheral rim. This curved surface (R) is desired toform a so-called uniform loaded curve. An uniform etching is achieved bythis curved surface (R). In other words, the back side of semiconductorwafer 13 is contacted completely to electrode 14 through a cooling gas,as will be mentioned later. Clamp ring 15 is arranged along the rim oflower block electrode 14. It is sized to contact the peripheral rimportion of semiconductor wafer 13 with the convexed surface of lowerblock electrode 14 through the cooling gas. It is made of aluminium, forexample, having its surface processed with anodized aluminum and coatedwith insulating alumina. It is lifted and lowered by a lift system (notshown) to press semiconductor wafer 13 above the lower block electrode14 at a pressure a little higher than the pressure of the cooling gasgushed from the electrode 14.

Lower block electrode 14 is provided with four through-holes 16, forexample, vertically passing through electrode 14. Lifter pin 17 ishoused in each of through-holes 16. Lifter pin 17 is made of SUS andfour lifter pins 17 are freely lifted and lowered together with plate 18from which lifter pins 17 are erected and which is driven by lift system19. When not driven by lift system 19, plate 18 is urged downward bycoil spring 20. The top of each of lifter pins 17 is held lower than theupper surface of lower block electrode 14. Cooling gas flowing pipe 21is connected to through-holes 16. It is also communicated with plural orsixteen openings 22 which are arranged on that portion of the uppersurface of lower block electrode 14 which correspond to the peripheralrim portion of semiconductor wafer 13. Cooling gas introducing pipe 23connected to a cooling gas supply source (not shown) is located underreaction container 1 to supply a cooling gas such as cooled helium gasto the underside of semiconductor wafer 13 through openings 22 andthrough-holes 16. As a result, semiconductor wafer 13 is held by acooling gas gushed from the electrode 14.

When electric power is applied to lower block electrode 14, electrode 14is heated similarly to the case of upper electrode 7. A cooling systemor passage 24 is thus provided, contacting the underside of lower blockelectrode 14. Pipes 25 connected to passage 24 is communicated with e.g.a liquid cooling device (not shown) to circulate cooling liquid or waterthrough pipes 25 and passage 24. Lower block electrode 14 may be cooledby the forced air cooling system, natural air cooling system orelectrical cooling system, as stated above about upper electrode 7.Lower block and upper electrodes 14 and 7 are electrically connected toRF power source 26.

Exhaust ring 28 provided with exhaust hole 27 is fitted between the sideof lower block electrode 14 and the inner face of reaction container 1.Exhaust pipe 29 extending from one side of reaction container 1 underexhaust ring 28 is connected to an exhaust device (not shown) to exhaustgas from the inside of reaction container 1. Etching apparatus 30 hasthe above-described arrangement.

Substrate or semiconductor wafer 13 to be processed is conveyed intoreaction container 1 through a lock room (not shown) from a wafercassette of a convey system (not shown). This conveying of semiconductorwafer 13 is achieved according to a predetermined program. Semiconductorwafer 13 is received in higher position than the position of electrode14, by lifter pins 17 which have been lifted higher than the uppersurface of lower block electrode 14 by lift system 19 throughthrough-holes 16. When lifter pins 17 is lowered (or when electrode 14is uppered), semiconductor wafer 13 is contacted with the upper surfaceof lower block electrode 14 through the cooling gas gushed from theelectrode 14. Semiconductor wafer 13 is pressed against lower blockelectrode 14 at the peripheral rim portion thereof by clamp ring 15. Andsemiconductor wafer 13 is held along with the cooling gas existingbetween the wafer 13 and the electrode 14. The upper surface of lowerblock electrode 14 is curved (R) or convexed. Even when semiconductorwafer 13 is caused to have warp or flexure in the previous process,therefore, it can be reliably contacted with the upper surface of lowerblock electrode 14 through the cooling gas. Reaction container 1 is madeair-tight and vacuum to a desired extent. This process of makingreaction container 1 vacuum may be previously carried out, using anauxiliary chamber, at the time when semiconductor wafer 13 is to beconveyed into reaction container 1. As a result, whole the back sidesurface of semiconductor wafer 13 is contacted uniformly to electrode 14surface through the cooling gas.

Block electrode 4 is then lowered by lift system 2 through connectingrod 3 to held upper electrode 7 and lower block electrode 14 separatedfrom each other by a desired distance or several millimeters to generateplasma, for example. Reaction gas such as freon gas and argon gas issupplied from the gas supply source (not shown) to space 8 through gassupply pipe 9. The reaction gas supplied to space 8 flows to the surfaceof semiconductor wafer 13 through plural holes 10 in upper electrode 7.High frequency electric current is applied at the same time from RFpower source 26 to upper electrode 7 and lower block electrode 14 tochange the reaction gas to plasma. Semiconductor wafer 13 is etched bythis plasma of the reaction gas. Upper electrode 7 and lower blockelectrode 14 are heated by the high frequency electric current applied.When upper electrode 7 is heated, it undergoes thermal expansion. Upperelectrode 7 is made of amorphous carbon while block electrode 4contacted with this upper electrode 7 is made of aluminium. Therefore,they are different from each other in thermal expansion coefficient andcrack is caused in one of these electrodes 7 and 4. In order to preventupper electrode 7 from being cracked, the cooling means (not shown)allows cooling water to flow into block electrode 4 through pipes 6 andpassage 5 to cool upper electrode 7 indirectly.

When lower block electrode 14 is heated, the temperature ofsemiconductor wafer 13 is also raised. This may cause the resist patternon the surface of semiconductor wafer 13 to be damaged. Similarly to thecase of upper electrode 7, cooling water or the like is fed from thecooling means (not shown) into lower block electrode 14 through pipes 25and passage 24. This cooling water is controlled to have a temperatureof 20° to 80° C. so as to enable semiconductor wafer 13 to be processedat a certain temperature. Semiconductor wafer 13 is also heated by thethermal energy of plasma. Semiconductor wafer 13 is therefore cooled insuch a way that cooling gas such as helium gas is supplied from thecooling gas supply source (not shown) to the underside of semiconductorwafer 13 through gas introducing pipe 23, gas flowing pipe 21, plural orsixteen openings 22 along the peripheral rim of lower block electrode 14and four through-holes 16 at the center of electrode 14. Openings 22 andthrough-holes 16 are closed this time by semiconductor wafer 13 but aslight clearance is left between semiconductor wafer 13 and the uppersurface of lower block electrode 14. Helium gas is supplied into thisclearance to cool semiconductor wafer 13. As a result, semiconductorwafer 13 doesn't contact with the surface of lower electrode 14directly. The slight clearance is filled with the cooling gas.Therefore, the temperature of the semiconductor wafer 13 is set to adesired low value.

FIGS. 2A, 2B and 2C are intended to obtain optimum values about thepressure and flow rate of helium gas. It was assumed that the vacuumdegree of reaction container 1 was 2.4 Torr, output of RF power source26 500 W, flow rate of freon gas which served as the reaction gas was 80cc/min., and flow rate of argon gas 500 cc/min. The flow rate of heliumgas which served as the cooling gas was changed from 3 cc/min (FIG. 2A)to 5 cc/min (FIG. 2B) and 8 cc/min (FIG. 2C). Temperature was measuredat center C and other two points E₁ and E₂ in the peripheral rim portionof semiconductor wafer 13. As shown in FIG. 2B, temperature became equalat points C, E₁ and E₂ on semiconductor wafer 13 when the flow rate ofhelium gas was 5 cc/min and the pressure thereof was 7.5 Torr. It istherefore understood that uniform etching can be applied to the surfaceof semiconductor wafer 13 when the flow rate and pressure of helium gasare these values.

FIG. 3 shows an example of the control system for the cooling gas orhelium gas. The flow rate of helium gas is adjusted to a desired valueby flow rate adjusting controller 31 and flow rate adjuster 32associated with flow rate adjusting controller 31 then automatically sethelium gas, which is fed from gas supply source 33, to have this desiredvalue of flow rate. Helium gas whose flow rate has been adjusted issupplied to the underside of semiconductor wafer 13 through valve 35,which is closed and opened by solenoid 34a, pipe 36 and gas introducingpipe 23 in lower block electrode 14. Pressure monitor or manometer 37for detecting the pressure of flowing helium gas is attached to pipe 36.Pressure information detected is inputted to pressure controller 38.This pressure controller 38 closes and opens control valve 39 responsiveto pressure information inputted. Control valve 39 is on pipe 41connected to vacuum means 40 and it is connected to pipe 36 throughvalve 42 which is driven together with valve 35 by solenoid 34a. Whenthis control valve 39 is driven, helium gas can be set to have thedesired pressure.

Pipe 43 for making pressure same at the underside of semiconductor wafer13 and in reaction container 1 after semiconductor wafer 13 is processedis arranged between reaction container 1 and pipe 36. Valve 44 which isdriven by solenoid 34b is on pipe 43 and it is opened when pressure isto be made same at the underside of semiconductor wafer 13 and inreaction container 1. When valve 44 is opened, solenoids 34a and 34b areinverted to stop the supply of helium gas while to make pressure same atthe underside of semiconductor wafer 13 and in reaction container 1.

The uniformity of etching can be enhanced when the pressure and flowrate of cooling gas supplied to the underside of semiconductor wafer 13is controlled as described above.

This uniformity of etching is influenced by the force of clamp ring 15with which semiconductor wafer 13 is pressed at the periphery rimportion thereof and also by the position of openings 22 on the surfaceof lower block electrode 14. When four openings 22 are arranged at thecenter of the surface of lower block electrode 14, as shown in FIG. 4A,the characteristic of semiconductor wafer 13 is as shown in FIG. 4B.When four openings 22 are arranged at the center of lower blockelectrode 14 and other sixteen openings 22 at the peripheral rim portionthereof, as shown in FIG. 5A, the characteristic of semiconductor wafer13 is as shown in FIG. 5B. It was assumed in FIGS. 4B and 5B that thepressure or vacuum degree in reaction container 1 was 2.4 Torr, outputof RF power source 26 500 W, flow rate of freon gas which served as thereaction gas was 80 cc/min, flow rate of argon gas 500 cc/min,temperature of upper electrode 7 20° C., and temperature of lower blockelectrode 14 lower than 8° C. The flow rate and pressure of cooling gasfor lower block electrode 14 was changed from 2 cc/min and 10 Torr inFIG. 4A to 5 cc/min and 7.5 Torr. Temperature was measured at one pointC in the center and other two points E₁ and E.sub. 2 in the peripheralrim portion on the surface of semiconductor wafer 13 while changing thedriving pressure of clamp ring 15. As apparent from FIGS. 4B and 5B, thetemperature distribution of semiconductor wafer 13 becomes more uniformwhen openings 22 are also arranged at the peripheral rim portion oflower block electrode 14. Further, it is found that temperature becomesequal at points C, E₁ and E₂ on semiconductor wafer 13 when the setpressure of clamp ring 15 is 6.0 kg/cm².

It can be prevented by the supply of cooling gas, as described above,that semiconductor wafer 13 is heated by plasma generated to reduce theuniformity of etching. The temperature distribution of semiconductorwafer 13 can be made certain by this supply of cooling gas to enhancethe uniformity of etching.

Gas in reaction container 1 after the etching process and air inreaction container 1 at the time when semiconductor wafer 13 is to beconveyed into reaction container 1 are appropriately exhausted to theexhaust means (not shown), which is located outside the reactioncontainer 1, through hole 27 in exhaust ring 28 and exhaust pipe 29.

Although four openings have been arranged in the center of the lowerblock electrode while locating other sixteen openings at the peripheralrim portion thereof to supply cooling gas to the underside of thesemiconductor wafer through these openings, the number of these openingsis not limited to the above. Further, the supply of cooling gas has alsobeen carried out through those four openings in the center of the lowerblock electrode in which the lifter pins are housed, but these fouropenings in the center of the lower block electrode may be formedindependently of those ones in which the lifter pins are housed.

According to the etching method as described above, the flow rate andpressure of cooling gas supplied to the clearance between the substrateto be processed and the lower block electrode on which the substrate ismounted can be controlled to cool the substrate, so that temperature canbe made equal at every point on the substrate to enhance the uniformityof etching. Further, the pressure and flow rate of cooling gas can becontrolled to be desired values by monitoring the pressure and flow rateof cooling gas. Furthermore, even when the supply of cooling gas isstopped by accident, it can be detected and conquered to prevent theproductivity of the semiconductor wafers from being reduced.

The upper electrode is cooled by cooling means 31 in the case of theabove-described etching apparatus. As shown in FIG. 6, it may bearranged in this case that a means for detecting poor cooling or flowswitch 32 is located on pipe 6 to detect whether or not the flow rate ofthe cooling water which flows through pipe 6 is in a range of set valuesor whether or not the cooling water flows through pipe 6 and that ameans is provided to stop the generation of plasma when the flow rate ofthe cooling water is not in the range of set values or when the coolingwater does not flow through pipe 6. The means for stopping thegeneration of plasma is formed in such a way that whether or not theflow rate of the cooling water is equal to a set value or in the rangeof set values is detected by flow switch 32 and that when it is notequal to the set value or in the range of set values, flow switch 32 isopened to shut off electric current applied from RF power source so asto stop plasma discharge needed for the etching process.

The forced air cooling system in which air is cooled and circulated, thenatural air cooling system which uses radiating fins contacted withblock electrode 4, or the electric cooling system in which Peltiereffect elements are arranged in block electrode 4 may be employedinstead of the liquid cooling system in which a cooled and controlledliquid is used. The flow rate of air is monitored to detect poor coolingin the case of the forced air cooling system. The temperature of blockelectrode 4 is monitored to detect poor cooling in the case of thenatural air cooling system. The temperature of cooling elements orelectric current supplied is monitored to detect poor cooling in thecase of the electric cooling system. Same effect can be achieved in anycase.

Lower block electrode 14 and upper electrode 7 are connected to RF powersource 26 with flow switch 32 interposed between upper electrode 7 andRF power source 26. When flow switch 32 detects the poor cooling ofupper electrode 7, electric current supplied from RF power source 26 isshut off.

Upper electrode 7 and lower block electrode 14 are cooled as describedabove to achieve a stable etching process. When the cooling of upperelectrode 7 is poor, however, upper electrode 7 is cracked and thetemperature of semiconductor wafer 13 is changed by radiant heat toreduce the productivity of semiconductor wafers. This is the reason whyflow switch 32 is located on pipe 6, as the means for detecting the poorcooling of block electrode 4, to detect whether or not the flow rate ofthe cooling water which flows through pipe 6 is in a range of set valuesor whether or not the cooling water flows through pipe 6. This is alsothe reason why another means is provided to stop the generation ofplasma when the flow rate of the cooling water is not in the range ofset values. According to this means for stopping the generation ofplasma, the above-mentioned detection is carried out by flow switch 32and when the flow rate of the cooling water is not equal to a set valueor in the range of set values, flow switch 32 is opened to shut offelectric current supplied from RF power source 26 so as to stop plasmadischarge needed for the etching process. This stop of current supplyprevents upper electrode 7 from being cracked. It also preventssemiconductor wafer 13 from being subjected to any undesirable influencein the course of the etching process. The stop of the etching processmay be informed to operators by alarm sound or display.

The flow switch has been used as the means for detecting poor cooling inthe etching apparatus shown in FIG. 6 and it has been detected by thisflow switch whether or not the flow rate of the cooling water whichflows through the pipe is in a range of set values or whether or not thecooling water flows through the pipe. However, the detecting system ofpoor cooling is not limited to this. It may be arranged that atemperature detecting means such as the thermistor thermocouple andthermograph is attached to the block electrode or upper electrode andthat the temperature of the block electrode or upper electrode ismonitored by this means to stop the generation of plasma when thetemperature is not in a range of set values.

The etching apparatus of the present invention can be applied to the CVDapparatus, ion injection apparatus, sputtering apparatus and the like toachieve same effect as described above.

According to the etching apparatus shown in FIG. 6, the block electrodeprovided with an upper electrode which is opposed to another lower blockelectrode on which a substrate to be processed is mounted is cooled bythe cooling means and when the poor cooling of the block electrode isdetected by the detector means, the generation of plasma or supply ofelectric current is stopped to prevent the block electrode and upperelectrode from being abnormally heated by current supplied. When theabnormal heating is stopped like this, it can be prevented that theupper electrode made of such a material that is quite different from thematerial of the block electrode in thermal expansion coefficient iscracked by the thermal expansion of the block electrode, therebyenabling the durability of the etching apparatus to be enhanced. Whenthe abnormal heating is stopped and the temperature of the upperelectrode is controlled by the cooling means, the temperature of thesubstrate to be processed can be kept certain, giving no undesiredinfluence to the etching process.

What is claimed is:
 1. A method for cooling a plasma electrode systemfor an etching apparatus, comprising the steps of:holding an object tobe processed, above a lower electrode opposed to an upper electrodewithin a vacuum container, to form a clearance between the lowerelectrode and the object; attaching said upper electrode to exchangeheat with a block electrode; supplying a cooling gas to said clearanceformed between the lower electrode and the object; supplying a coolantinto said block electrode; controlling at least one of a flow rate orsupply pressure of said cooling gas; supplying a process gas into saidvacuum container, in order to generate a plasma; and controlling atleast one of a flow rate or supply pressure of said coolant in order todetect the change in temperature of said coolant during the process andto decrease the amount of deformation caused by heat.
 2. The methodaccording to claim 1, wherein means for holding the object above thelower-electrode with the clearance is a support gas gushed from theinside of the lower electrode towards the vacuum container with apredetermined pressure.
 3. The method according to claim 2, wherein thepressure of the gushed support gas is a little higher than aclamp-driving pressure for clamping the object.
 4. The method accordingto claim 2, wherein said support gas is gushed only into said clearancebetween the object and the lower electrode.
 5. The method according toclaim 1, further comprising means for controlling the temperature of thefurther comprising said block electrode, said temperature-controllingmeans controlling the temperature of said block electrode in accordancewith the change in temperature of said coolant.
 6. The method accordingto claim 1, wherein a flow rate of the cooling gas to said clearance iscontrolled.
 7. The method according to claim 1, wherein said upperelectrode is made of amorphous carbon, and said electrode is made of Alor Al alloy.
 8. The method according to claim 1 wherein said upperelectrode is made of the material whose thermal expansion coefficient isdifferent from that of said block electrode.
 9. The method according toclaim 1, wherein said upper electrode is screwed on said blockelectrode.
 10. The method according to claim 1, wherein said cooling gasis helium gas.
 11. The method according to claim 1, wherein said coolantis supplied to a region which is in the vicinity of a connection memberbetween said upper electrode and said block electrode.
 12. The methodaccording to claim 1, wherein said upper electrode has a large number ofgas holes in the center thereof, and the periphery of said upperelectrode is fixed to said block electrode.
 13. A method for cooling aplasma electrode system for an etching apparatus, comprising the stepsof:holding an object to be pressed, above a lower electrode opposed toan upper electron within a vacuum container, to form as clearancebetween the lower electrode and the object; attaching said upperelectrode to exchange heat with a block electrode; supplying a coolinggas to said clearance formed between the lower electrode and the object;supplying a coolant into said block electrode; controlling a flow rateor supply pressure of at least one of said cooling gas and said coolant;supplying a process gas into said vacuum container, in order to generatea plasma; and controlling the operation of plasma etching process inorder to detect the change in temperature of said coolant during theprocess and to decrease the amount of deformation caused by heat.